Can multiple animations be saved in a .blend file?
I think your issue is that Blender is not saving the animation datablocks because there aren't any objects using them. You can protect the datablocks by adding a fake user like so:

Go to the NLA editor

Select the Action

Open your properties panel (N)

In the top panel (Animation Data) select the action you want to protect from the dropdown.

Click the F next to the name to give the action a fake user:



Alternatively this can be done in the header of the Dope Sheet editor while in Action Editor mode.